In sheet metal vehicle bodies, the rear end is typically assembled by welding together a number of preformed metal sheets to form a bearing structure having an encasing outer wall. In most instances, a cross member is provided for connection to both the floor of the trunk and to the ends of the longitudinal bearers in the region where they emerge into the rear end portion of the vehicle body.
Such a construction is relatively costly, due to the larger number of sheet metal parts and welding steps required. Furthermore, since the entire interconnected arrangement is usually deformed in the event of a rear collision, repair costs are also expensive and cost-intensive.
In known rear end designs of the type comprising a pair of transverse members including an upper transverse member and a lower transverse member joined together one above the other, and wherein the transverse members each have a constant cross section and the lower transverse member is joined to a trunk floor, a substantial portion of the lower transverse member contour lies above the level of the trunk floor. In addition, the lengthwise members provided on each side of the vehicle terminate in the region in front of the rear wheel housings. Since the rear end is joined by many structural pieces to the wheel housings, side walls, helical springs, etc., the impact energy associated with a commonly occurring rear collision from a sideways direction correspondingly acts on a number of parts, including the load-bearing frame elements. Thus, even a vehicular collision of a relatively low impact energy will cause major damage, thereby resulting in high repair costs for straightening out and replacing the many damaged sheet metal components.
U.S. Pat. No. 1,809,606 discloses a vehicle frame structure wherein two longitudinal members are joined by rivet connections by a middle cross member and a rear cross member. The middle cross member has curved ends, each of which abut on one of the opposing inward facing walls of the two longitudinal members. The rear cross member is straight and is flush mounted at right angles to the rear ends of the longitudinal members.
Other arrangements for the load bearing frame elements of a vehicle space frame are known, such as, for example, from International Publication No. WO 90/02680 (corresponding to International Application No. PCT/NO89/00086), wherein each load bearing longitudinal structural member is formed as an integral extruded multicavity shape which is split, selectively curved, and aligned to merge with secondary complementary shaped members. A portion of each of the multicavity shaped members diverges from the longitudinal direction to form front and rear cross members, however, no compound cross member having means for reducing impact energy is disclosed or suggested.
Repairs are especially problematic for the known vehicle bodies which have space frames assembled from extruded aluminum sections and cast joint elements, an example of which is disclosed in European patent document EP 0 146 716. Such aluminum bodies are extremely long-lived on account of the increased resistance to corrosion as compared to conventional sheet metal bodies. Based on present day accident statistics, it is safe to assume that such long-lived vehicle bodies will likely experience repeated damage with deformations, especially in the rear end, during the average course of its lifetime. Repairs, especially repairs of the aluminum load-bearing frame elements, are particular problematic on account of the known difficulties, such as expensive light metal welds and loss of strength at welded points in the case of multiple welds. Therefore, it is desirable to provide structural solutions which protect against damage caused to the vulnerable collision points of the load-bearing frame elements in a light-metal vehicle body particularly in the event of commonly occurring minor collisions having less serious impact energies.